The purpose of the present study is to increase host resistance against his tumor by providing him with selected cell populations of lymphoid cells capable of specifically or non-specifically attacking the tumor. The first step will be to better define the roles of lymphoid cell subtypes in tumor immunity, and to determine which cellular interactions lead most directly to tumor destruction. Procedures will be adapted or developed to increase the populations of cells that interact with the tumor in a detrimental fashion, and to decrease the populations of cells that interfere with tumor destruction, or in any way protect the tumor. These include cells which are directly inhibitory, or which inhibit indirectly by producing antibody components of blocking factor. Alterations in the activity of lymphoycte populations will be measured in terms of lymphocyte stimulation and cellular cytotoxicity in vitro and tumor neutralization or regression of established tumors in vivo.